ESP32 FreeRTOS task crashes: 'Stack canary watchpoint triggered' and tasks that return

Both errors show up as soon as you move work into your own tasks with xTaskCreate() / xTaskCreatePinnedToCore(), in ESP-IDF and in the Arduino core alike.

1. Stack canary watchpoint triggered (task_name)

The named task wrote past the end of its stack. ESP-IDF places a canary/watchpoint at the end of each task stack and stops the moment it's touched.

Fix: create the task with a larger stack.

xTaskCreatePinnedToCore(measureTask, "measure", 8192 /* bytes on ESP32 */, nullptr, 1, nullptr, 1);

• Minimal stack sizes are far too small for anything using Serial, Wi-Fi, TLS, JSON libraries or printf-style formatting.
• Large local buffers (char buf[2048]) live on the stack; make them static or allocate them once.
• Then measure instead of guessing: uxTaskGetStackHighWaterMark(nullptr) from inside the task reports the smallest amount of stack that has remained free. Trim only with a safety margin.
• Note: on ESP-IDF the stack depth argument is in bytes, unlike vanilla FreeRTOS (words).

2. The task function returns

A FreeRTOS task function must never simply return. On ESP32 this crashes (the error mentions that the task should not return).

void measureTask(void *arg) {
  for (;;) {                        // long-running tasks loop forever
    takeMeasurement();
    vTaskDelay(pdMS_TO_TICKS(1000));
  }
}

void oneShotTask(void *arg) {
  doWorkOnce();
  vTaskDelete(nullptr);             // one-shot tasks delete themselves
}

Related

• A task that never blocks (no vTaskDelay, no waiting on a queue) starves others and trips the task watchdog; see the Inter-AI item on the ESP32 task watchdog.

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